Here’s what closes down and what doesn’t.

The House and Senate had until midnight on Friday, January 19, to pass a spending bill before the federal government ran out of money and closed its doors.

Despite controlling every lever of government, Republicans are somehow faced with the possibility that they can’t get the votes together to keep the government open.

It’s been more than four years since the last government shutdown, but after copious experience with shutdowns, especially during the protracted budget standoffs of the Clinton and Obama presidencies, we have a good sense of what will happen to the federal government.

What a government “shutdown” looks like

Attorney General Benjamin Civiletti, who laid out what modern government shutdowns look like, with Jimmy Carter in 1979. Walter Bennett/The LIFE Picture Collection/Getty Images

When Congress can’t pass some kind of appropriations bill before a spending deadline, the government shuts down, and many “nonessential” government activities suddenly cease.

It’s not unusual for Congress to go to the brink of shutdown; it happened as recently as this past fall, when President Trump threatened a shutdown in a bid to get funding for a border wall.

The government has officially shut down 18 times since the modern process that Congress uses to pass budget and spending bills took effect in 1976. The first six of those didn’t actually affect the functioning of government at all. It wasn’t until a set of opinions issued by Attorney General Benjamin Civiletti in 1980 and ’81 that the government started to treat “spending gaps” — periods when Congress has failed to allocate funds for the ongoing functions of government — as necessitating the full or partial shutdown of government agencies.

But from the Reagan years onward, any period in which Congress failed to pass funding measures has meant that major chunks of the government stop operating. Which parts differ from shutdown to shutdown, but it generally excludes essential services without which the economy would grind to a halt and people would die.

During shutdowns, federal employees are divided into “essential” and “nonessential” groups (the official wording was changed to “excepted” and “non-excepted” in 1995 to avoid hurting people’s feelings). Nonessential personnel receive furloughs: They’re off work until the shutdown is resolved and stop receiving paychecks.

In the October 2013 shutdown, about 850,000 federal workers received furloughs, or about 40 percent of all federal nonmilitary employees. After shutdowns, furloughed workers almost always receive retroactive payments covering their salaries during the shutdown. Essential workers also see their pay withheld — but they have to work anyway.

Who is exempted, and not exempted

Despite President Trump’s tendency to point to the military as the biggest victim of a potential shutdown, it’s not — the military is, of course, generally considered “essential” to the functioning of the US government.

And just as law enforcement agents have become the domestic mirror image of soldiers in conservative identity politics, they’re also considered essential employees across all government agencies. Air traffic control, federal prisons, and Social Security and other benefit payments also generally keep functioning as normal during shutdowns.

But many other government functions are curtailed. In the 2013 shutdown, the effects of the furloughs and other shutdowns in government activity included:

Federal research activities at the National Institutes of Health (which lost about three-quarters of its employees), the National Science Foundation (which lost 98 percent of its workforce), and the Centers for Disease Control and Prevention (which lost two-thirds) shut down nearly entirely; the CDC scaled back its monitoring of disease outbreaks.

The Food and Drug Administration delayed approval of drugs and medical devices.

The national parks shut down, resulting in $500 million in lost consumer spending from tourism.

Reviews of veterans’ disability applications slowed to a halt, with nearly 20,000 applications per week not being evaluated.

In total, the Office of Management and Budget estimated that the shutdown cut GDP growth in the fourth quarter of 2013 by 0.2 to 0.6 points, and resulted in 120,000 fewer jobs.

So while shutdowns don’t result in seniors going without their retirement checks, or the military closing up shop, or airplanes crashing into each other in the sky, they do cause massive disruption in the lives of hundreds of thousands of workers and their families, and grind a lot of government agencies to a halt.

Immigration agencies are slowed down

The exception for law enforcement means that the overwhelming majority of Border Patrol, customs officers, and Immigration and Customs Enforcement agents will remain on duty through a shutdown — and that the Trump administration’s stepped-up enforcement of immigration laws, including greater arrests of immigrants without criminal records, is as essential as anything else.

But it isn’t in itself essential to facilitate legal immigration to the US. US Citizenship and Immigration Services will largely be unaffected by the shutdown simply because it doesn’t get its money from Congress; it’s funded by the fees it charges applicants. But companies seeking work visas for their employees might run into trouble, because the Department of Labor office that needs to approve their petition would be closed.

Overseas, consular offices, while they could stay open over a brief shutdown by running off fee money, could end up being closed if the shutdown is prolonged — making it impossible for people in those countries to get approved to come to the US until the government reopened.

And while the US Refugee Admissions Program isn’t technically subject to shutdown, the Obama administration stopped bringing refugees to the US during the 2013 shutdown anyway, because of the anticipated difficulty getting Social Security cards and other vital resources to refugees once they arrived in the United States. Feeding refugees is considered an essential function of the State Department, but resettling them permanently isn’t on the same level.

That’s an appropriate balance if you think the parts of the US government that exist to punish lawbreakers are more essential to day-to-day operations than the parts that allow people to follow the laws. But that is, itself, a skewed view of what’s most important about the government — and about who can afford to wait for days or weeks while a shutdown is resolved in Washington.

A government that provides routine inspections and generates information isn’t “essential”

Not all “law enforcement” or security efforts are created equal under shutdown plans, of course, and regulatory agencies are generally given short shrift.

Drug Enforcement Administration and Bureau of Alcohol, Tobacco, and Firearms field offices are exempt from shutdowns; many Food and Drug Administration officials working on investigations, however, are not. The TSA is fully exempt, but the Centers for Disease Control and Prevention had to furlough a large fraction of its staff. Civil litigation efforts at the Department of Justice (including antitrust investigations) would cease; the Occupational Safety and Health Administration and the Mine Health and Safety Administration would be, temporarily, all but gutted.

In a way, all of these are either security or law enforcement functions of government. But the “essential” government doesn’t think that every official whose job is to check compliance with the laws is an essential one — even if those laws could, in theory, be protecting people from health and safety hazards.

At OSHA, the FDA, and the Mine Health and Safety Administration, for example, what gets shut down are “routine” inspections and investigations. Emergency efforts — mines near collapse, large-scale food or drug recalls — can proceed or be initiated, but the day-to-day compliance efforts that are supposed to prevent those emergencies from happening can’t.

For progressives who see consumer protection as an important function of the federal government, this is arbitrary, even insulting (though partisans can take some glee in knowing that the Consumer Financial Protection Bureau itself is unaffected by shutdown). For libertarians and business-minded conservatives who see overregulation and red tape as a serious chilling effect on entrepreneurship in America, it’s an (admittedly extreme) version of the regulatory state they’d like to see to begin with.

And then there are the parts of the government dedicated primarily to the production of knowledge — a function that’s been underappreciated in the past, but that has come to the fore as worries have spread that the Trump administration is neglecting it. At the Environmental Protection Agency, where administrator Scott Pruitt is openly contemptuous of employees and where some employees have all but started smuggling out data before it gets destroyed, the overwhelming majority of staff would be furloughed.

The Bureau of Labor Statistics would stop releasing reports, as would the Bureau of Justice Statistics. Work at the US Census Bureau, which is already behind in preparations for the 2020 census, would grind to a halt.

These are things that people who care about “good government” care about. They’re not, for the most part, high priorities for people who care about “small government.”

This might explain why, as a shutdown looms, the burden is often perceived from the outside to be on Democrats to avoid it — not just because they’re the ones, in this case, refusing to vote for a bill that keeps the government open for another few weeks but doesn’t provide a permanent solution for Deferred Action for Childhood Arrivals (DACA) recipients, but because they’re the ones who believe most firmly that these “nonessential” government functions really are essential.

Government is made of people

But given all this, it’s important to remember: Not even the most radical small-government ideologue in Congress ever prefers shutting down the government to keeping it open on their terms. That’s because when a shutdown actually happens, it calls attention to the fact that government is made of people — and that those people are both more interdependent on each other (even the “nonessential” ones) and less politicized than the functions they represent.

Even “essential” employees at FEMA or the US Border Patrol, for example, suffer setbacks in morale and job function when they don’t have any support staff to help them, because the field agents are “essential” but support staff is not. The military may itself be deemed essential, but delays in paychecks, and the inability to request leave, can grind down service members and their families.

The same is true on the other side: Americans who interact with the government for benefits. Older middle-class Americans might be better off than those living in poverty under a shutdown, because Social Security and Medicare are exempt (not congressionally appropriated) while Temporary Assistance for Needy Families may not — but if they lose their Social Security cards, they won’t be able to get new ones issued.

It’s a broad truth of American politics that people may not like “government” in the abstract, but they like the particular ways government benefits them. Shutdowns bring that dynamic to the fore: They force people to reckon with the fact that while concepts like “cutting the fat” and “waste, fraud, and abuse” are broadly appealing, agreeing on what counts as fat or waste is much harder.

And it makes apparent that living in uncertainty day to day isn’t actually a way to go about one’s life, whether one is a government employee or someone whose life is in a government employee’s hands.

The government that survives a shutdown is a government that is much more hobbled in some respects than others, but it isn’t the government anyone wants.